High end Class D amps?

It's Fremer. If a dog looked like a turntable, he would claim its bark sounded like Pavarotti. I take anything he says with a bottle of salt.

He also says audiophiles are wasting time playing with preamps, amps, cables, etc, while ignoring room acoustics and speakers. The real audiophiles keep saying it's all about room acoustics and speakers. The ones that start threads and blather on about cables, fuses, cable risers, etc., Etc. .... We'll make your own conclusions.

https://www.soundandvision.com/content/bruno-putzeys-head-class-d-page-2

And queue inane EPDR comment ....

Right on clue(less)

"Class-D likes benign 4-6ohm loads with low - phase angles, and that’s what the Maggie’s are, but when the loads get tough, then big Linear Amps come out to play."

Why would a Class-D amp care about phase angle? Many have higher impedance at high frequencies which could come into play but the phase angle of the speaker load would have no impact.

There is only one so far that has taken Class-D and it’s operation to the technology edge, that "could" even better the best Class-A or A/B’s.
And that is the Technics SE-R1 that uses linear power supplies, the latest GaN devices, and has taken their "switching frequency" nearly 3 x higher than any other Class-D’s have so far, which means 3 x far less switching frequency residual noise and all important phase shift at the speaker terminal outputs.

Cherry Amps already switch up to 2Mhz which is faster than the Technics.
3x switching frequency does not mean 3x less noise. That's a factor of switching frequency AND filters.

I will repeat my question, why would a class-D amplifier care about phase angle. The data you have presented only applies to thermal loading (hence dissipation resistance) in the linear region of semiconductor devices (It would apply to tubes as well, but don't think it would be much of an issue). Class-D semiconductor devices operate in saturation and would not be impacted by this.

That value that you quote, EPDR has absolutely nothing to do with max current requirement. It is a synthetic value to represent thermal loading in a linear amplifier. It has no application to Class D amplification.

I suggest going back and understanding this better as your understanding is flawed.

I will state again. You clearly do not understand what this term EPDR means. It had absolutely no meaning for a class D amplifier as it does not work in the linear range.  The only figure that matters is lowest impedance which in most speakers occurs where Class D amplifiers have very low output resistance.

Your request for tests from 8 to 1 ohm is meaningless and again has no relation to EPDR and a Class D amplifier.

Whether they current limit or not is representative of maximum power and designed thermal limits. What matters is THD at those power levels.

Until you increase your knowledge of Class D amplifiers and this term EPDR as it applies to amplifiers I feel this conversation will go no where. Unfortunately your knowledge in this area is not sufficient for us to have a meaningful conversation.

You see @georgehifi, @jaytor understands quite clearly how your term EPDR has no meaning effectively for Class D as well as how your metric of doubling in output power at half the output load impedance has little meaning for Class D. You do not. You don’t appear to possess adequate knowledge in this area. This is very basic stuff.  Please research amplifier topologies more if you have the skill set and you will see how misguided you are

I currently don’t make, sell, or market any amplifiers and have no skin in the game either way. I do understand quite well amplifier topology though.

georgehifi, given your obviously thin educational knowledge w.r.t. amplifier topologies and again obviously without the practical experience to compensate for that knowledge gap, perhaps you should be giving pause to the fact that people with far more knowledge of amplifiers theoretically and practically are all telling you you are wrong. Not just one, but everyone.

This goes beyond Dunning-Kruger it is just bizarre. We aren't arguing over something subjective or subject to opinion. This is clear cut, basic operational details.  It is almost at conspiracy level.  I don't understand it.

I generally think of the Odyssey units more as PA amplifiers than serious audiophile gear. Throw lots of brute force at a problem, but not a lot of finesse ending up with a "warm" but bloated sounding box.  If that is the sound you like, then I am not surprised the Cherry was not to your liking. It is transparent, not "euphonic".

 Bruno is a promoter, but unlike many in the audio industry, actually has the technical chops to put something together.


Switching frequency was important 10+ years ago before people figured out putting the filter inside the feedback loop.

The claim the output filter is "deadly" to euphonics, again is "old" knowledge, see last comment about the placement of the filter in new higher end class-D amplifiers, not to mention a bit better practical understanding of how to tune class-D filters, however, keep in mind the filter is to keep ultrasonics out of the speaker.

George is coming from a position of near 0 experience with actual class-D amplifiers and I expect almost 0 experience at the architectural / design side of amplifiers at all.  He only knows what he reads, with limited direct listening experience.  Because he does not have the right experience or knowledge, he misinterprets what he reads and draws erroneous conclusions.  He is not "holding his ground", he is standing in one place stomping his feet up and down.  

As others have pointed out, there are Class-D amplifiers that sound excellent, and not just the one that george is enamored with, and likely only from knowing 1 raw specification about that amplifier. George isn't calling anything out.


I am currently listening to a Cherry amplifier and I must say, I am rather impressed with it.

madavid0141 posts12-01-2020 11:20pmI don't know it seems to me that George is coming from a position of a lot of experience and the fact that he's holding his ground here suggests to me that he's on the right side while you guys are just compensating with confirmation bias and group-think. Many people don't care at all about what is true, only that they feel good about something, so when someone is willing to call out something as being garbage many people won't want to hear it.

Technics GaNFET: Dry, sterile, boring. Burned it in for over a month. The cheap integrated unit.

I don’t claim to know all the Technics GaNFET units, but I am not aware of a "cheap" integrated unit and considering you are using relatively "cheap" Odyssey Stratos, I am not sure what you consider cheap. Even a new Cherry is a fair amount more money than a standard configuration Stratos. Do you mean the G700 which I don’t think uses GaN. SU-G30? .... that is $4,000.

The way to tell people who know and don't know what they are talking about is by the detail and depth of their posts.  Ralph, jaytoy, and I talk about architectural specifics about Class-D, even where the filter is placed. We talk about device operating region. We talk in numbers specific to Class-D.   One other person here who has a bugaboo and about Class-D and I think Ralph in general does not.  I would argue that he cannot, and if he educated himself, he still would not be able as he would see his errors.

As Ralph has pointed out, there are many ways to skin the Class-D cat. High frequency open loop is just one method. Claiming it is the best is like claiming tubes of solid state is the best.  We know many do it, but it is purely dogmatic.  Implementation details can push either in a direction of like or dislike for a given person.

Tim also clearly laid out what I would agree w.r.t. modern high end class-D. It is targeted towards very neutral. Many don't like that.  I am finding the Cherry very neutral. It does appear to have a better supply than what you are using.  I have heard your present Odyssey a few times, one of my friends bought on reviews and did not keep it.  I can see the allure, but it was not for him and and if you like that sound, the Cherry may not be your cup of tea, and I can't recommend one that will be, though they may be out there. 

There was very good "power DAC" technology 15 years ago. As fewer and fewer analog sources are in play, this will become more and more dominant.


I am sure George will find reasons to put down these two amplifiers you linked, but alas, no description of how EPDR or anything else matters.

YOU are not one of the best designers. You are not even a designer. I would highly doubt you are an engineer.

Rules that apply to linear amps, do not apply to Class-D. As well, how well feedback works is a matter of amount of feedback, loop gain, and gain bandwidth.

The "best" designers are few and far between and they say things like this as generalities AND to sell THEIR amplifiers. They also only say them about non-class D amplifiers.

It is NOT used just locally either, it is used locally or globally, and both. Both work. Depends what sound you are trying to achieve and what your design parameters are.

Most discrete linear audio amplifiers are really quite simple. You think your music was recorded through low, local only feedback amplification chains after the microphone? Get real.

It is not 1973 or 1974 any more and no one is talking about Kenwood, but your ideas and knowledge seem to come from 1974.

And yes, throwing speakers in the loop is exactly where this is all going. Subwoofers with position and velocity feedback are already here and research is moving this up the frequency spectrum.

George see's one graph, or reads one article and he thinks that automatically applies to everything with the same basic name. That is technical ignorance talking.

georgehifi7,965 posts12-02-2020 5:53pm
Problems with any amps shouldn’t be fixed by using even more feedback as a fix, it’s a added by the best designers to clean thing up a little and usually just local not global in an already well designed amp.

All the greatest amp designers say it. An amp should be reasonably good spec’d, and to use it just as a clean up tool.
And the preference with the best is to use "local feedback" only by the best designers. Not global as being talked about here, and then even including the Class-D output filter in the global loop, what next throw the speaker wire and the speaker in the loop as well, like Trio/Kenwood tried all those years ago, utter sterilized disaster sound.

And using tube buffers with the capacitor coupling that’s needed. Is just colorized HF coverup softening job for the more serious Class-D sound problem.

Cheers George

I will throw and old dog a bone ... namely I will throw you a bone George.

Explain, in detail please, exactly how EPDR impacts the ability of Class-D amplifiers to drive a load.

That is it, that is all you need to do.  I am 100% certain you can't do it correctly, but here I am, have the floor, grab the bone, and show everyone you are the expert.  Tell us exactly how EPDR impacts a Class-D amplifiers ability to drive a load.

Oh george, now you are resulting to lying.

Georgehifi  CAN NOT tell people here why EPDR matters to a Class-D amplifier because he does not understand Class-D, he does not understand EPDR, and he does not understand SOA.   Given his hate for Class-D, if he truly understood these things, he would be all over this given clear, concise and accurate explanations. He does not, because he can't.

And now you are calling me a "fuser". Anyone here can read my posts and readily see that I am not a "fuser". Of course that does not change the fact you don't understand electricity either. "AC" is not an argument for fuses not being directional. It is because fuses are not directional that AC operation is not impacted. It is NOT a subtle distinction.

georgehifi7,971 posts12-02-2020 11:24pm

And there you have it folks.

You have nothing but your ignorance and being a fuser, and your persistence in the

At the price points, or close, the best of Class-D is every bit competitive to the best of the other classes. Calling me a Class-D flag waver is funny. I am doing nothing but pointing out your ignorance on a topic you are very passionate about, but know little about.

At the level of performance of good Class-D (which does not need to be very expensive), you really are just talking about preferred flavor.

You continued posting of old, and wrong information seems to know no bounds. When you have to use ignorance or perhaps lies to make an argument, that tells a lot. Why do you do it?
The one who have proved repeatedly they have no idea is you.  Quick search shows you have been on this wrong-headed EPDR crusade for what, 2+ years, and still you don't understand it.  Ditto your class-D crusade with repeated postings of large phase-shift from an older technology Class-D amp. Ditto your insistence that Class-D must have phase-shift if the switching frequency is not MHz plus. Ditto your insistence that feedback must be bad (even though that is from a different architecture with different constraints). Ditto your insistence that doubling with reduction in ohms is essential to good sounds, without any consideration to what that means and why it normally does not matter, even with a low impedance load. Maybe you can't teach an old dog new tricks.

And there you have it folks.

Throw the old dog a bone and he chokes on it. Georgehifi has clearly stated he is unable to explain how EPDR will impact a Class-D amplifiers ability to drive a load. I hate to say I told you so, but I told you so.
Hint to the old dog, there is nothing in that article that relates to Class-D.

Do you even know how to read an SOA graph? I am going to guess no. You don’t understand this graph:

https://www.stereophile.com/images/archivesart/707HL_Fig3.jpg


In a Class-D amplifier, the voltage across the device is effectively 0 (or close to it). That means the devices operates on the graph effectively on the left vertical axis at 0 volts. The limitation is pretty much the device current rating. Practically it will be a bit to the right of that as there is dissipation due to RDSon and partial conduction for nanoseconds while switching.

Funny you can find tons of time to attempt to bust every Class-D thread and to chase fusers ad-nauseum, but you can't even put a few of your own words together to explain why EPDR could matter to a Class-D amp. I know why you don't. It is because you can't.  You would rather bash Ralph from Atmasphere and others not here to defend themselves with falsehoods. That is not honest behavior.

George, you are the one that needs to give it a break. You act like the Class-D police and fuse police, yet you don't even understand how Class-D works and you make up facts about Class-D that is not even true.  I will stop calling out your illogical and incorrect attacks on Class-D when you stop making them.

George, keep digging that hole. I am not the one spreading false information in a one man crusade against something I don't understand, that is you. If your only refuse is attempted personal attacks, then I suggest you exit this argument which you are clearly unprepared for. It is time to let this Class-D crusade go. You are the knight without a sword riding a lame horse.

Is there a moderator in the house?

Hey moderator, this @georgehifi character pollutes every single Class-D thread with tons of messages making a claim that is totally wrong. This must be the 3rd of 4th thread just since I joined.

@georgehifi,

I am not going anywhere.

Your repeatedly attempts to use EPDR shows you have no idea what it means and how it relates to amplifiers, and I would say contrary to what Atmasphere said, it does not apply at all to Class-D as the FETS in Class-D do not operate in the linear region, hence the phase has no bearing on the thermal loading of a Class-D amplifier.


As well, Class-D amplifiers may not double in power intentionally, as they may intentionally current limit. That is not a bad thing and has no impact on sound quality if you are not driving into clipping and there is no stability issue. Your repeated attacks against something you clearly don’t understand really needs to stop.

It’s rare that someone will state so clearly that the don’t understand what they are arguing about. As a monument, I will place this here.

Hint for George, EPDR is NOT a measure of current loading. It is a measure of equivalent thermal loading. Unless the load is a resistive only, this will ALWAYS happens somewhere other than where the current is at a maximum.

georgehifi8,069 posts12-15-2020 6:09pm

George - You’ve brought up this notion of EPDR in several class D threads, but haven’t explained how it relates to class D.

It relates to any amplifier seeing the low EPDR loading which demands extra current to be delivered from the amp, which Class-D’s don’t do as well as good linear Bi-Polars can.

Ricevs, I believe Millercarbon has already claimed the title of Master of self Promotion. Perhaps you can choose a new title?

There is nothing wrong with a 3 terminal regulator if followed with adequate filtering. It will be sonically transparent especially if driving a stage with feedback.

I am sure you have measurements that justify your claim of "purer"?

No all regulators do not have "a sound". Circuit implementations have a sound. Even a properly implemented low cost 3 terminal regulator implemented properly will be sonically transparent.

So what you are saying is NO you don’t have measurements. So pure is just your personal taste, not an accurate unbiased assessment. Thank you for clearing that up.

At an electronic level pure can be measured. Given you have no measurements your claim of pure is only that, a claim. You feel it is. I may think it sounds more colored.

I am judging. Too many audiophiles claim to be seeking sonic accuracy because they tweak this or tweak that, meanwhile their listening space is a disaster and they have more money into cables than their speakers.

So basically, it's a fire hazard?

Solid walnut backplate. No, aluminum does not sound the same.

Try using a wooden j-box in your house and telling the electrical inspector he is an idiot because the wires inside it are insulated.

There is no "fire hazard".....same with having cotton covered wires inside.

... It won't work with the safety inspector nor UL, ENEC, etc.

All those protections on the supply are not definitive protections from catastrophic events. There is a reason why electrical products are encased in metal or fire retardant plasics.

Your source better have low output impedance as well. The NC500 modules are fairly low impedance on the input.

georgehifi8,196 posts01-03-2021 9:17pmOr even better if your source has balanced output and enough gain, feed it direct into the NC500 amp modules with no buffers at all, like I did, with my NC500 monoblocks. This is the least distortion and most transparent/dynamic you’ll get

See what I mean @mike_in_nc

Hopeless case.

George does not understand class D and even though I have tried to educate him he refuses to learn.  I expect some statement now about EPDR. It will be wrong.